Whenever the percentage of the motor vehicle fund arising from excise taxes on motor vehicle and special fuels payable into the bond retirement fund proves more than is required for the payment of interest on bonds when due, or current retirement of bonds, any excess may, in the discretion of the state finance committee and with the concurrence of the department, be available for the prior redemption of any bonds or remain available in the fund to reduce requirements upon the fuel excise tax portion of the motor vehicle fund at the next interest or bond payment period.